The B cell maturation antigen (BCMA) is member 17 of the tumor necrosis factor receptor superfamily (TNFRSF). Its native ligands are the B cell activating factor (BAFF; also called BLyS or TALL-1, TNFSF13B) and a proliferation-inducing ligand (APRIL, TNFSF13, CD256) which are involved (through interaction with further ligands) in regulating various aspects of humoral immunity, B cell development, and homeostasis.
BCMA is highly expressed on malignant plasma cells, for example in multiple myeloma, (MM), which is a B cell non-Hodgkin lymphoma of the bone marrow, and plasma cell leukemia (PCL), which is more aggressive than MM and constitutes around 4% of all cases of plasma cell disorders. In addition to MM and PCL, BCMA has also been detected on Hodgkin and Reed-Sternberg dells in patients suffering from Hodgkin's lymphoma (Chiu et al. (2007) Blood 109:729-739). Similar to its function on plasma cells, ligand binding to BCMA has been shown to modulate the growth and survival of multiple myeloma cells expressing BCMA (Novak et al. (2004) Blood 103:689-694). Signalling of BAFF and APRIL via BCMA are considered as pro-survival factors for malignant plasma cells; hence, the depletion of BCMA-positive tumour cells and/or the disruption of ligand-receptor interaction should improve the therapeutic outcome for multiple myeloma and autoantibody-dependent autoimmune diseases.
There are presently various approaches available for the treatment of multiple myeloma (Raab et al. (2009) Lancet 374:324-339). Chemotherapy leads in most subjects only to partial control of multiple myeloma; only rarely does chemotherapy lead to complete remission. Combination approaches are therefore often applied, commonly involving an additional administration of corticosteroids, such as dexamethasone or prednisone. Corticosteroids are however plagued by side effects, such as reduced bone density. Stem cell transplantation has also been proposed, using one's own stem cells (autologous) or using cells from a close relative or matched unrelated donor (allogeneic). In multiple myeloma, most transplants performed are of the autologous kind. Such transplants, although not curative, have been shown to prolong life in selected patients (Suzuki (2013) Jpn J Clin Oncol 43:116-124). Alternatively thalidomide and derivatives thereof have recently been applied in treatment but are also associated with sub-optimal success rates and high costs. More recently, the proteasome inhibitor bortezomib (PS-341) has been approved for the treatment of relapsed and refractory MM and was used in numerous clinical trials alone or in combination with established drugs resulting in an encouraging clinical outcome (Richardson et al. (2003) New Engl J Med 348:2609-2617; Kapoor et al. (2012) Semin Hematol 49:228-242). The costs for combined treatments are correspondingly high and success rates still leave significant room for improvement. The combination of treatment options is also not ideal due to an accumulation of side effects if multiple medicaments are used simultaneously. Novel approaches for the treatment of plasma cell diseases, in particular multiple myeloma, are required.
The ability to specifically target plasma cells is also of great benefit for the treatment of autoimmune diseases. Mild forms of autoimmune disease are usually initially treated with nonsteroidal anti-inflammatory drugs (NSAID) or disease-modifying anti-rheumatic drugs (DMARD). More severe forms of Systemic Lupus Erythematosus (SLE), involving organ dysfunction due to active disease, usually are treated with steroids in conjunction with strong immunosuppressive agents such as cyclophosphamide, a cytotoxic agent that targets cycling cells. Only recently Belimumab, an antibody targeting the cytokine BAFF, which is found at elevated levels in serum of patients with autoimmune diseases, received approval by the Food and Drug Administration (FDA) for its use in SLE. However, only newly formed B cells rely on BAFF for survival in humans, whereas memory B cells and plasma cells are less susceptible to selective BAFF inhibition (Jacobi et al. (2010) Arthritis Rheum 62:201-210). For rheumatoid arthritis (RA), TNF inhibitors were the first licensed biological agents, followed by abatacept, rituximab, and tocilizumab and others: they suppress key inflammatory pathways involved in joint inflammation and destruction, which, however, comes at the price of an elevated infection risk due to relative immunosuppression (Chan et al. (2010) Nat Rev Immunol 10:301-316, Keyser (2011) Curr Rheumatol Rev 7:77-87). Despite the approval of these biologicals, patients suffering from RA and SLE often show a persistence of autoimmune markers, which is most likely related to the presence of long-lived, sessile plasma cells in bone marrow that resist e.g. CD20-mediated ablation by rituximab and high dosage glucocorticoid and cyclophosphamid therapy.
Antibodies which bind CD269 (BCMA) and their use in the treatment of various B-cell related medical disorders have been described in the art. Ryan et al (Molecular Cancer Therapeutics, 2007 6(11), 3009) describe an anti-BCMA antibody obtained via vaccination in rats using a peptide of amino acids 5 to 54 of the BCMA protein. WO 2012/163805 describes BCMA binding proteins, such as chimeric and humanized antibodies, their use to block BAFF and/or APRIL interaction with BCMA and their potential use in treating plasma cell malignancies such as multiple myeloma. The antibody disclosed therein was obtained via vaccination in mouse using a recombinant peptide of amino acids 4 to 53 of the BCMA protein. WO 2010/104949 also discloses various antibodies that bind preferably the extracellular domain of BCMA and their use in treating B cell mediated medical conditions and disorders. WO 2002/066516 and WO 2012/066058 disclose bivalent antibodies that bind both BCMA and additional targets and their potential use in the treatment of B cell related medical disorders. Details regarding the binding properties and specific epitopes of the bivalent antibodies are not provided in either disclosure.